When used to generate photographic quality images, cathode ray tube scan systems traditionally have problems producing good scan linearities. As a result, the resulting photographs are distorted in that elements at the edges of the scanned images are larger than identical elements at the center of the image. It is known that such distortions are more noticeable, and thus more objectionable, in hard copy images, e.g. still photographs, than they are in moving images such as television images.
Flat face electrostatic focus cathode ray tubes are also known to require different focus voltages at different distances from the center of the tube face. It is therefore necessary to provide a dynamic focus correction voltage signal with a circuit which is less expensive than the analog integrated circuits presently used.